Most of what a devops person does is in fact development but it is of the non value adding variety. Basically a devops person spends the vast majority of their time configuring common off the shelf software, scripting this or that, etc.
A singular matrix is a matrix which has no inverse because its determinant is zero. If you recall, the inverse of a matrix is. 1/ ad-bc multiplied by: [ d -b ] [-c a ] If ad-bc = 0, then the inverse matrix would not exist because 1/0 is undefined, and hence it would be a singular matrix. E.g.
A singular $3\times 3$ real matrix maps $\mathbb{R^3}$ into a proper subspace of $\mathbb{R^3}$ (a plane through the origin, a line through the origin, or, most degenerately, to just the origin). A non-singular matrix maps $\mathbb{R^3}$ onto itself.